Apparatus and method to feed and preheat a metal charge to a melting furnace

Abstract

An apparatus to feed and pre-heat a metal charge to a melting furnace of a steelworks comprises a feeding and pre-heating tower separate from the melting furnace provided with at least one compartment to temporarily contain said metal charge, transfer means to transfer said metal charge to said melting furnace and conveying means to convey the fumes exiting from the melting furnace to said compartment. The apparatus also comprises a post-combustion chamber, disposed adjacent to and below said compartment, and connected on one side to said compartment and on another side to said conveying means the post-combustion chamber being configured to determine the expansion of the fumes introduced by the conveying means and to direct said expanded fumes toward said compartment along a path such as to determine a desired residence time of said fumes suitable to obtain at least the substantial complete combustion of the unburned gases present in said fumes.

Description

FIELD OF THE INVENTION[0001]The present invention concerns an apparatus and the corresponding method to feed and pre-heat a metal charge to the melting furnace of a steelworks.BACKGROUND OF THE INVENTION[0002]Apparatuses are known, for feeding a metal charge to the melting furnace of a steelworks. Before being fed to the furnace, the metal charge or scrap is normally pre-heated by means of the fumes produced by the melting of the metal.[0003]Some known apparatuses provide a feeding and pre-heating tower for the scrap, integrated with the furnace and disposed directly above it, such as for example in the solution shown in JP 61 015908 A, so that the scrap is discharged from above directly into the liquid bath, with obvious problems, given the quantities of metal charge fed on each occasion, even 40 tonnes, of splashing of the liquid bath and slag, given the height, even 4-5 meters, from which the metal charge is discharged, and also problems of transmission of knocks and vibrations f...

AI Technical Summary

Benefits of technology

The present invention provides a method for safely and efficiently melting metal charges by using a post-combustion chamber to prevent explosions and remove carbon monoxide before fumes are introduced into the atmosphere. The post-combustion chamber also allows for the sedimentation of particulate and powders, resulting in a better heat yield and reduced energy expenditure. Additionally, the post-combustion chamber can be positioned to provide a longer residence time for the fumes and greater freedom in modulating the temperature and duration of the residence time. The invention also includes a shutter means for gradual and progressive discharge of the metal charge from the compartment to the transfer means.

Problems solved by technology

Some known apparatuses provide a feeding and pre-heating tower for the scrap, integrated with the furnace and disposed directly above it, such as for example in the solution shown in JP 61 015908 A, so that the scrap is discharged from above directly into the liquid bath, with obvious problems, given the quantities of metal charge fed on each occasion, even 40 tonnes, of splashing of the liquid bath and slag, given the height, even 4-5 meters, from which the metal charge is discharged, and also problems of transmission of knocks and vibrations from the tower to the furnace during these steps.

These known apparatuses have the main disadvantage, however, that the early contact of the fumes with the scrap, given their short journey, does not give the necessary time for completing the combustion of the fumes, which therefore, when they come into contact with the metal charge, are still rich in carbon monoxide because it has not been completely combusted into carbon dioxide.

This causes, first of all, the risk of explosions in the metal charge with the danger of compromising the functionality of the process, the integrity of the plant and the safety of the workers.

Furthermore, after the pre-heating step there is a presence of carbon monoxide in the fumes directed to the flue, which entails more risks of explosions along the pipes and also the need to provide appropriate and costly systems to remove the carbon monoxide before the fumes are introduced into the atmosphere, since carbon monoxide is notoriously a dangerous and toxic pollutant.

Another disadvantage of known devices is that the metal charge is put in contact with the fumes when they are still very hot, and this risks causing the small-size components of the metal charge and the components that melt at low temperatures to melt already in the first part of the feed tower.

If this melting occurs in the zone where the metal charge is introduced inside the electric furnace, compact blocks are formed that cause blockages in the conveyor pipe, with consequent long and complex interventions to reactivate the plant.

Another disadvantage of known apparatuses is that the fumes which hit the metal charge directly at high temperature, comprised between about 1,200° C. and about 1,350° C., cause high levels of oxidation of the metal charge.

The oxidation reduces the yield of the metal charge and frustrates the beneficial effect of recovering the energy of the fumes, since a greater electric energy is required in order to melt the oxidized metal charge in the furnace.

Moreover, the high losses of load that affect the fumes along their path inside the pre-heating chamber have the disadvantage of requiring apparatuses to be installed that have greater power, so as to induce the motion of the fumes from the chamber to the exit flue.

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